Automatic load-responsive governing device



Dec. 21, 1 954 TURNER 2,697,556

7 AUTOMATIC LOAD-RESPONSIVE GOVERNING DEVICE Filed March 25, 1952 2 Sheets-Sheet l Dec. 21, 1954 G. TURNER 2,697,556

AUTOMATIC LOAD-RESPONSIVE GOVERNING DEVICE Filed March 25, 1952 2 Sheets-Sheet 2 I N Il AUTOMATIC LOAD-RESPONSIVE GOVERNING DEVICE This invention relates to governing devices and has for an improved form thereof.

In many cases a working machine such, for instance, as a grinder of material fed thereto by a mechanical feeder, is driven by an electric motor which runs at constant speed and which operates at maximum efiiciency only when fully loaded. The material fed to the machine on the other hand may vary in character so that at a fixed speed of the mechanical feeder the load on the motor will vary correspondingly with an adverse effect upon its efiiciency.

An object of the present invention is the provision of a device that will ensure that when in operation the driving motor of the machine is always loaded to a predetermined degree.

The present invention consists in an automatic load responsive governing device for controlling the load on a working machine, including in combination a substantially constant speed source of power and a control shaft driven thereby through a slipping clutch, means for braking the control shaft in accordance with the load on the working machine and means for adjusting the load on the said machine in accordance with the speed of revolution of the control shaft.

The slipping clutch may be of the fluid type using air as the medium connecting the driving and driven members of the clutch.

The control shaft braking means may comprise a metal member fixed to and coaxial with the control shaft and arranged so that part of the said member is engaged by an electro-magnetic field the strength of which field varies in accordance with the driving current of a constant speed electric motor which energises the working machine.

The load on the working machine may be adjusted by a variable feed device for the said machine regulated in accordance with the speed of the control shaft.

ne way of carrying the invention into effect by way automatic load-responsive an object the provision of of example will now be described and illustrated by the accompanying diagrammatic drawings in which:

Figure l is a sectional elevation of a control unit.

Figure 2 is a sectional elevation of the same control unit on the lines AA viewed in the direction of the arrows.

Figure 3 depicts a diagrammatic arrangement showing the governing device applied to a working machine.

Referring to Figures 1 and 2 of the drawings, the control shaft 1 is keyed to the rotor 2 and carries a pulley 3.

The rotor 2 has a cylindrical metal rim 4 which closely approaches the pole pieces 5, 6 and 7 of an electro-magnet 8. Tangential blades 9 are formed on both of the inner flat surfaces of the rotor 2.

Similar tangential blades 10 are formed on each side of a central disc 11 and have only a small clearance from the blades 9 and the inside of the cylindrical part 4 of the rotor 2.

The disc 11 with its blades 10 is keyed to the shaft 12 of a constant speed electric motor 13, and a substantially cylindrical casing 14, surmounted by a rectangular casing 15 enclosing the electro-magnet 8, is secured to the casing of the motor 13.

Self-aligning ball bearings are arranged as shown in Figure 1 between the casing 14 and the shaft 1 and between rotor 2 and the motor shaft 12.

The blading 10 on the member 11 is so arranged that when rotated by the motor 13 the air in the enclosed United States Patent 0 2 circulates in a closed circuit outwardly through the spaces between the blades 10 and inwardly through the blades 9 and so drives the rotor 2, the arrangement acting as a fluid coupling or clutch.

The electro-magnet 8 is energised in accordance with the driving current of a constant speed electric motor which drives the working machine, and its eddy-current braking effect on the rim 4 of the rotor 2 will vary according to the said driving current, thus the electro-mag net constitutes a brake.

Referring more particularly to Figure 3 in conjunction with Figures 1 and 2, the coil 16 of the electro-magnet 8 is shown in series with the current flowing through the constant speed motor 24 by way of the main supply 25', 26.

The motor 24 drives the which material is fed through the inlet 22 to emerge in a desired condition from the outlet 23.

The material is fed from a hopper 20 by means of a conveyor belt 19, the rollers 18 of which are driven by the pulley 3 of the control device shown in Figures 1 and 2, by way of the belt 17. The conveyor 19 may be replaced by other controllable mechanical means for feed- ;ngdthe machine 21, such for instance as a rotary or shaker ee er.

In operation, when no material is being fed to the machine 21, the current demand of the motor 24 will be very light, the corresponding current through the electromagnet coil 16 will be small and the eddy-current braking effect of this magnet on the rim 4 of the rotor 2 will be negligible. The speed of the rotor 2 will, therefore, lag very little behind that of the impeller 11 on the shaft 12 of the constant speed motor 13.

If now material is fed in increasing quantity to the conveyor belt 19, the load on the grinding machine will increase with consequent increase of the driving current of the motor 24-the electro-magnet 8 will be increasingly energised and the braking effect upon the rotor 2 will increase with a corresponding decrease of the speed of the control shaft 1 and of the conveyor belt 19.

When the flow of material to the grinding machine 21 reaches a value which demands the full load current of the driving motor 24, the supply of material to the machine 21 is stabilised and, assuming that the material is of a uniform character, the entire apparatus will operate without fluctuation at a rate which fully loads the driving motor.

Should the material supplied to the grinding machine alter in character so that it becomes more diificult to grind with a tendency to overload the driving motor, increased braking due to increases in the current in the electrospace in the rotor of the more difficult material.

Conversely, the advent of a material less difiicult to grind would result in a speeding up of the control shaft and of the supply to the grinding machine until the same stable conditions of fully loading the driving motor are reached.

The invention is not limited to the particular grinding machine assembly described, or to a clutch having air as a slipping medium and any suitable form of braking of the control shaft may be employed. Also additional manually controlled braking may be employed to vary the load condition about which regulation takes place for instance a further electro-magnetic brake of manually variable value may be applied to the rotor on the control shaft.

I claim:

1. An automatic load responsive governing device for controlling the load on a working machine driven by a constant speed electric motor which governing device comprises a slipping clutch having driving and driven members, a second constant speed electric motor connected to the driving member of the clutch, means connected to the driven member of the clutch adapted to adjust the load on the working machine, a brake associated with the driven member of the clutch, means responsive to the load on the working machine adapted to increase the braking effect with increase of load and to 

